The invention relates to a system for reducing aerodynamic noise at a supplementary wing of an aircraft hinged to a main wing and extendable to open a gap between the main wing and the supplementary wing.
Modern commercial aircraft have high-lift components in the form of supplementary wings, such as, for example, movable slats or landing flaps provided on the front edge of the main wing which are actuated during takeoff and landing for increasing the lift at low speeds. These supplementary wings are hinged to the main wing, and may be extended when a gap region between the main wing and the supplementary wing is opened. A significant problem is that when the supplementary wing is extended, considerable aerodynamic noise is generated due to turbulent flow in the gap region which is perceived to be very objectionable, in particular at ground level.
A channel is provided on the back side of a slat, for example, in which in the extended state of the slat a flow separation region of the gap flow develops in the form of a vortex. This vortex is constantly supplied with new energy from the adjoining gap flow. Turbulence balls enter the accelerated gap flow via a separation flow line between the vortex flow region and the gap flow, generating noise. However, noise is radiated through the outward flow of the turbulence balls over the rear edge of the slat.
Various systems are known from the prior art for reducing this aerodynamic noise at the supplementary wing of a commercial aircraft, in which a separating surface is provided which can be moved into the gap region when the supplementary wing is extended and which is elongated in the direction of the span width and extends at least partially along a separation flow line between the vortex flow region and a gap flow of the air flowing in the gap region between the supplementary wing and the main wing.
A supplementary wing for the main wing of aircraft is known from German Patent Document DE 199 25 560 A1, for example, in which such a system is provided for reducing aerodynamic noise in the form of a separating surface situated on the supplementary wing which extends in the direction of the main wing and runs along a separation flow line between the vortex flow region and the gap flow of the air flowing between the supplementary wing and the main wing. This separating surface may have a rigid form, whereby it is hinged to the supplementary wing and is pivotable when the supplementary wing is retracted on the main wing, or when the angular position of the separating surface must be modified when the pitch angle of the aircraft changes. On the other hand, the separating surface may also have a flexible design, for example in the form of an inflatable balloon or displacement body which is affixed to the supplementary wing and which may be impinged on with pressure when the supplementary wing is extended.
A system for reducing aerodynamic noise at a slat of a commercial aircraft is known from German Patent Document DE 100 19 185 A1, for example, in which a hollow displacement body is provided in a profile curvature, adapted to the outer contour of the main wing, on the back side of the slat which by use of a controlled bleed air line is optionally inflatable, thereby forming a separating surface which separates the vortex flow region from the gap flow in the gap region between the slat and main wing.
In a further system for reducing aerodynamic noise at a slat of a commercial aircraft, known from German Patent Document DE 101 57 849 A1, a separating surface which extends partially along a separation flow line between the vortex flow region and the gap flow of the air flowing in the gap region between the supplementary wing and the main wing is formed from multiple brush hairs, arranged in series, which are distributed over the span width of the slat and are aligned in at least one row.
A further system for reducing aerodynamic noise at a slat of a commercial aircraft is known from German Patent Document DE 100 19 187 C1, in which a separating surface between the vortex flow region and the gap flow of the air flowing in the gap region between the supplementary wing and the main wing is formed by a displacement body which may be inflated by bleed air.
The disadvantage of systems in the form of flaps, sheets, or the like is that such structures are usually not able to sufficiently mask or cover the vortex flow region. Noise-radiating turbulence may form at another location. In addition, a complicated kinematic actuator system is necessary for actuating and controlling such structures.
Although inflatable structures having elastic or “soft” surfaces may conform well to the desired contour, implementation in a technical system is difficult. Complicated valve connections are usually necessary to control the air intake and exhaust. In addition, when bleed air is used, special materials must be chosen due to the high temperature of the bleed air which is typically equal to or greater than 280° C. A further disadvantage is that suitable elastic materials are susceptible to aging and damage and are not resistant to UV radiation, which significantly limits the useful life and greatly increases the maintenance effort.
The present invention, therefore, provides an improved system for reducing aerodynamic noise at a supplementary wing of an aircraft, which in particular has a simple design and which may be operated easily, reliably, and consistently. A further aim is that the system is reliable with respect to breakdowns.
Advantageous embodiments and refinements of the system according to the invention are described below. In one exemplary embodiment, the invention provides a system for reducing aerodynamic noise at a supplementary wing of an aircraft which is hinged to a main wing and is extendable when a gap region between the main wing and the supplementary wing is opened. The system has a separating surface which can be moved into the gap region when the supplementary wing is extended and which is elongated in the direction of the span width and which extends at least partially along a separation flow line between a vortex flow region and a gap flow of the air flowing in the gap region between the supplementary wing and the main wing. According to the invention, the separating surface is an n-stable surface which by using an actuator device can be moved between at least one of the stable states and at least one additional state.
The exemplary approach according to the invention allows the channels in supplementary wings or main wings which produce vortex flows on the aerodynamically active surface to be moved in a simple manner so that the formation of turbulence is completely or significantly reduced.
According to one advantageous embodiment of the system according to the invention, the separating surface is a monostable (n=1) surface which automatically assumes a stable state from which it may be moved by actuation of the actuator device.
The monostable separating surface may be designed such that it automatically returns to the stable state when the actuation of the actuator device ceases or breaks down. This has the advantage that breakdown protection is ensured in a simple manner, since the separating surface may be moved from its stable state to an additional state only by actuation of the actuator device, and resides in this additional state only for as long as the actuator device is active. When the actuation ends, i.e., when the actuator device is inactive, which may also be caused by a breakdown of the actuator device, the separating surface automatically returns to its stable state.
In its stable state the monostable separating surface preferably assumes a position that is retracted from the gap region and in which the supplementary wing is retractable on the main wing when the gap region is closed, and when the gap region is opened by extension of the supplementary wing as the result of or during the actuation of the actuator device, the monostable separating surface assumes an advanced position in which the separating surface at least partially separates the vortex flow region from the gap flow or occupies the space thereof. This has the advantage that if the actuator device breaks down, the separating surface automatically returns to its retracted position so that the supplementary wing may easily retract in an emergency. The latter must be ensured to comply with safety requirements for commercial aircraft.
It is practical for the monostable separating surface to be made of a material having spring-elastic structural properties. Alternatively or additionally, further devices, in particular a spring device (elastic spring, foam, or the like) may be provided whose action causes the separating surface to automatically return to its stable state.
According to another advantageous embodiment of the system according to the invention, the separating surface is a bistable (n=2) surface having two stable states between which the separating surface may be moved by actuation of the actuator device. This has the advantage that the actuator device need be activated only for moving the separating surface from a stable state to another stable state. The two stable states are each maintained without influence by the actuator device or influence by actuating forces, which simplifies control of the actuator device and optionally reduces the power consumption thereof.
This exemplary embodiment is preferably designed in such a way that in one of its stable states the bistable separating surface assumes a position that is retracted from the gap region and in which the supplementary wing is retractable on the main wing when the gap region is closed. In its other stable state, when the gap region is opened by extension of the supplementary wing, the bistable separating surface assumes an advanced position in which the separating surface at least partially separates the vortex flow region from the gap flow or occupies the space thereof. In this embodiment, breakdown protection is advantageously ensured by the fact that the supplementary wing during an emergency retraction presses against the extended or advanced separating surface, with the result that in a manner of speaking the separating surface is “snapped” and converts to its other stable state, the engaged or retracted state.
The two stable states of the exemplary bistable separating surface may be automatically established by virtue of the spring-elastic structural properties of the separating surface, by locking devices—as used in bicycle connections, for example—and/or by separate devices, in particular a spring device.
According to further advantageous embodiments, the separating surface is an n-stable (n≧3) surface which is able to assume n (n≧3) stable states, between which the separating surface is movable by actuation of the actuator device. For example, n may be advantageously 3, 4, 5 . . . or 10.
It is practical for the n-stable separating surface in at least one of its stable states to assume a position that is retracted from the gap region, in which the supplementary wing is retractable at the main wing when the gap region is closed, whereby when the gap region is opened by extension of the supplementary wing the n-stable separating surface assumes an advanced position in which the separating surface at least partially separates the vortex flow region from the gap flow or occupies the space thereof.
For the exemplary n-stable (n≧3) separating surface, the n-stable states may advantageously be automatically established by locking devices, as previously described in conjunction with a bistable separation surface, and/or by additional devices, in particular a spring device (elastic spring, foam, or the like).
According to one advantageous embodiment of the invention, the separating surface is a surface that at least partially covers the vortex flow region and is supported in an articulated manner on at least one side or fixedly clamped on at least one side, along a line running in the direction of the span width.
According to an alternative advantageous embodiment of the invention, the separating surface is a surface that at least partially or completely covers the vortex flow region and is supported on both sides along lines running in the direction of the span width.
According to one preferred embodiment, the dimensions of the separating surface between the lines running in the direction of the span width, along which the separating surface is supported, may be larger than the distance between these lines.
According to another embodiment of the invention, the separating surface may be supported in an articulated manner on both sides along the lines running in the direction of the span width.
According to an alternative embodiment, the separating surface is fixedly clamped on one side, and on the other side is supported in an articulated manner along a line running in the direction of the span width.
According to a further alternative, the separating surface is also fixedly clamped on both sides along lines running in the direction of the span width.
According to yet another advantageous embodiment of the invention, the separating surface is formed by a flexible planar material.
The planar material may be a flexible metal sheet, a fiberglass fiber-reinforced plastic (FRP), a carbon fiber-reinforced plastic (CRP), a fiber-reinforced polymer, or a fiber-reinforced elastomer.
The actuator device may include a rotary actuator which is coupled to the separating surface on at least one side on which the separating surface is supported, along the lines running the direction of the span width in order to move the separating surface between the at least one stable state and the at least one additional state.
The actuator device may also include a linear actuator which is coupled to the separating surface for moving it between the at least one stable state and the at least one additional state.
However, the actuator device may also include a fluid actuator which is coupled to the separating surface for moving same between the at least one stable state and the at least one additional state, the fluid actuator having a displacement body provided in the vortex flow region which may be impinged on by fluid.
The exemplary actuator device may be driven by a servomotor, an electric motor, or an electromagnet.
However, the actuator device may also be a pneumatic or hydraulic actuator.
The actuator device may have a single- or double-acting design, whereby “double-acting” is understood to mean that the actuator is able to produce force effects in opposite directions; i.e., the actuator may pull as well as push.
The actuator device may have a doubly or multiply redundant design.
According to a further embodiment, the actuator device may be designed as a cable, lever, drive pin, or the like, and the actuator device may be preferably kinetically coupled to an actuating device for retracting or extending the supplementary wing.
On the back side of the wing to which the separating surface is mounted, a channel is preferably provided in which the separating surface may be moved into a position that is retracted from the gap region and in which the supplementary wing may be retracted on the main wing when the gap region is closed.
It is particularly advantageous when the contour of the separating surface in the retracted position is adapted substantially to the contour of the channel.
According to one particularly advantageous embodiment of the invention, the supplementary wing is a slat or a landing flap.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.